1. Field of the Invention
This invention relates to a laminate adhesive and, more particularly, to a laminate adhesive which is useful for the manufacture of packaging materials for use in a variety of industrial fields, including packaging materials for food products, beverages, medical products and quasi-drags or packaging materials for electronic components such as hard disks.
2. Description of the Prior Art
Composite film produced by lamination of e.g. plastic film, metal foil of e.g. aluminum, metallized film, and silica evaporated film by use of an adhesive have been widely used as packaging material for use in a variety of industrial fields including packaging materials for food products, beverages, medical products and quasi-drags or packaging materials for electronic components such as hard disks up to the present date.
A two component ester urethane adhesive, using polyisocyanate in combination with polyester polyol or polyester polyurethane polyol, is used most as the laminate adhesive for the manufacture of these packaging materials, because of its excellent adhesion properties.
It is known, on the other hand, that polyester polyol produces by-products of cyclic ester compounds in the manufacture of it, and it has been hitherto believed to be hard to avoid the production of such by-products.
In recent years, there have advanced the studies on the substance to be eluted from packaging material into a content, which suggests the possibility that some low molecular weight compounds may be eluted from the adhesive into the content and the low molecular weight compounds thus eluted may attribute the cause, in part, to spoil the inherent properties of the content, such as the odor and taste of food products and beverages, or the inherent performances of the electronic components, though the cause and effect relationship has not yet been clarified.
It is the object of the present invention to provide a laminate adhesive that can suppress the elusion of a low molecular weight compounds of composite film into the content, so as to prevent the inherent properties or performances of the content from being spoiled by the low molecular weight compounds.